The spraycoating device is composed at least of a spray gun exhibiting the features of the present invention. However this invention also concerns a spraycoating device fitted in addition to said spray gun with a control unit or at least a sensor that are connected to said gun. A spray gun of this kind for coating liquid is known from the European patent document 1,048,359 A2. Moreover it is known from the field of practice to fit the spray gun with an electromagnetic sensor determining whether the valve element for the liquid of the liquid feed valve is situated in the closed or the open valve position. But electromagnetic sensors incur the drawback of being linked by a cable to the spray gun and by being electrically connected to said gun by an electric connector. Specifically said connector is susceptible to becoming defective because illustratively containing a small and easily deforming prong acting as the connecting element, and moreover said electrical cable increases the spray gun weight and degrades its freedom of motion.
Spray guns may be manual devices held manually or they may be automated and supported in a holder while being mounted in displaceable or stationary manner relative to an object. The holder may be a robot or a stand.
Spray guns typically are fitted with at least one electrode which is connected to a high DC voltage source for the purpose of electrostatically charging the coating liquid.
A comparable spray gun for coating liquid also is known from the German patent document 22 09 896 C2.
The above documents also disclose how to feed compressed air acting as atomizing air to the spray gun, in order to positively affect the atomization of the coating liquid, and/or to apply shaping air directed at the liquid sprayed from a spray nozzle in order to shape the spray jet, for instance in order to transform a cross-sectional circular spray jet into a cross-sectionally flat one and/or to prevent liquid particles from leaving the atomized spray jet. Before opening the liquid feed valve discharging and atomizing the coating liquid, the compressed atomizing air and the compressed shaping air already must have been applied in order that the coating liquid shall exhibit from its beginning the required shape and the spray jet quality necessary to optimally coat an object to be coated, because otherwise low quality of coating would ensue. As regards automated object coating, the objects are moved automatically past the spray guns. These spray guns are shut off in the gaps between the objects. In order to coat the objects from beginning to end at the proper quality, the application and shutting off (opening and closing) of the coating liquid and of the compressed atomizing air and/or of the shaping air must be accurately timed. This goal is attained in the state of the art by using electromagnetic sensors to detect the position of the liquid valve element relative to the valve seat for said liquid from the liquid feed valve.